Entrainment and Deposition of Surface Material by Particle-Laden Flows: From the Laboratory to the Hillslope

A non-technical description of the project's broader significance and importance

A debris flow is a dynamic moving mass of water, mud, soil and larger objects up to boulder size that is the main ingredient in a landslide. In steep hillslopes and mountainous regions a debris flow can travel over 160 km/hour (100 miles / hour) and can grow to over 20,000 m3 (700,000 cu.ft.), posing significant hazards to human life and infrastructure. Debris flows often begin as relatively small landslides that grow in size and speed as a result of the incorporation or entrainment of surface materials along its path. Knowing what influences the path, speed, and size of a debris flow will contribute toward the development of effective hazard mitigation practices. This project focuses on building a scientific basis for the processes that contribute to entrainment of surface materials by debris flows. Over much longer time scales, debris flows have contributed to shaping the landscape and directing the placement of certain mineral deposits, so documenting the controlling processes can contribute to more efficient location and acquisition of mineral resources. In addition, changing patterns of land use, climate, and human settlement may alter the magnitude and frequency of debris flows, so that knowledge of their mechanistic behavior will enable better modeling and prediction of their occurrence.

A technical description of the project

This project will use experiments, simulations, and field data to determine the importance of various mechanisms in debris flow entrainment and deposition, and the subsequent mobility from particle-scale effects to macroscopic dynamics. The research activities will determine the dominant mechanisms for entrainment as they may vary with scale. Experiments will be performed in smaller and larger flumes at the University of Minnesota and at the University of Natural Resources and Life Sciences in Vienna. The flumes are instrumented to monitor details such as pore pressures and stresses in the bed, and high-speed high-resolution cameras will capture flows as well as the evolution of the structure and entrainment of the bed materials. Field data will be gathered at an instrumented site with capabilities to measure forces, erosion, and kinematics such as the flow depth. Simulations will be performed with Discrete Element Method to help interpret dynamics inaccessible to the experiments. Results will be incorporated into a depth-averaged continuum model capable of predicting large scale debris flow dynamics. The relevance of the proposed research extends to a wide range of particle-fluid flows in nature and industry, including both subaerial and subaqueous flows, and particle processing across many industries. The educational and outreach component seeks to broaden participation and public comprehension of granular physics in general and applications to geophysics in particular through: (1) culturally sensitive educational materials developed for Fon du Lac Tribal camps for middle and high school students, (2) materials developed for the public through Science Buzz, an on-line site of the Minnesota Science Museum, where the investigator and students will post regularly and answer questions of the public about research and related current events and (3) actively involving undergraduates in research and outreach components, recruiting students of underrepresented groups through an established network of mentors at minority serving institutions and elsewhere.